This invention encompasses a conversion for spiral conveyor belt systems, by which a modular plastic conveyor belt is fitted onto a spiral tower designed for carrying a steel spiral conveyor.
Spiral conveyors have experienced increasing use in past decades particularly in the food industry, and they are also finding more and more uses in other manufacturing operations. They enable dwell time on a spiral tower in what is technically a helical path, the conveyor belt being driven up the curving incline in a low tension arrangement, primarily by engagement with a rotating driving tower at the center. Spiral conveyors initially, and for many years, comprised all steel belts, usually stainless steel for the food industry.
However, with the advent of plastic modular conveyor belts, capable of assembly in any length and virtually any width, some spiral conveyor belt systems were fabricated from modular plastic conveyor belts. Plastic materials have been developed for withstanding wide ranges of temperature, including high temperatures used in baking and other food processes and below-freezing temperatures, and spiral conveyors have been used for providing dwell times in desired environments, for cooling loaves of bread, for example, or for processing foods in other ways requiring an elevated-temperature environment. As examples of patents covering modular plastic conveyor belt systems, see KVP U.S. Pat. Nos. 4,901,844, 5,069,330, 5,310,045, 6,484,379 and 6,796,418.
A great many industries using steel spiral conveyor belt systems now desire to convert to modular plastic spiral conveyor systems. The plastic conveyor belts are not susceptible to corrosion, tend to be more easily cleanable and generally have smoother surfaces. Also, they have a lower coefficient of friction than steel, are lighter in weight and are more energy efficient due to the lower friction and lighter weight. They are easier to replace and repair, and most foods do not stick to plastic as they do to steel. In addition, steel belts as they wear tend to produce metal grindings, small particles of metal that can drop into the goods conveyed, which may be food products. This is unacceptable. However, the steel belts are not easily replaced with plastic because steel belts are generally stronger in beam strength through their width, and a typical track for a steel spiral conveyor has only two rails, or those for wider belts. If a plastic modular conveyor belt were fitted onto such a track with rails spaced apart as in a steel spiral system throughout the spiral path, a typical plastic modular conveyor belt would not support anything but a fairly light load on such a belt. In one solution to this problem, KVP in the above-referenced U.S. Pat. No. 6,796,418, in its SPIRAIL system, provides an easily installed retrofit kit for adding one or more additional rails to a spiral support track, thus enabling the use of plastic modular radius-type conveyors (such as those made by KVP) in a spiral system to support reasonably heavy loads.
See also U.S. Pat. No. 6,837,367, which shows a plastic modular belt for replacement of a steel belt in a spiral system. In that patented belt the center spine is enhanced in strength in the central region of the belt's width by being thicker (front to back) at that region than at both side edges.
It is an object of the current invention to provide a plastic modular conveyor belt which in itself has significantly increased beam strength to span between spaced apart rails such as typical of a steel spiral conveyor system, without the need for additional support rails, and at the same time to provide for smooth transfer of articles on and off the belt.